Materials for organic light emitting diodes

ABSTRACT

Compounds are provided that comprise a ligand having a 5-substituted 2-phenylquinoline. In particular, the 2-phenylquinoline may be substituted with a cycloalkyl containing group at the 5-position. These compounds may be used in organic light emitting devices, in particular as red emitters in the emissive layer of such devices, to provide devices having improved properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/932,546, filed on Jul. 1, 2013, which is a continuation-in-part ofU.S. patent application Ser. No. 13/006,016, filed on Jan. 13, 2011, nowU.S. Pat. No. 9,130,177, the entire contents of which is incorporatedherein by reference.

PARTIES TO A JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, The University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to organic light emitting devices (OLEDs).More specifically, the present invention is related to phosphorescentmaterials comprising a ligand having 2-phenylquinoline substituted witha cycloalkyl containing group at the 5-position. These materials may beused in OLEDs to provide devices having improved performance.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

Compounds comprising a 5-substituted 2-phenylquinoline containing ligandare provided. The compounds comprise a ligand L having the formula:

A is a 5-membered or 6-membered carbocyclic or heterocyclic ring.Preferably, A is phenyl. R_(A) may represent mono, di, tri, or tetrasubstitutions. Each of R_(A) is independently selected from the groupconsisting of hydrogen, deuterium, alkyl, silyl, alkoxy, amino, alkenyl,alkynyl, arylkyl, aryl and heteroaryl. R_(B) is selected from the groupconsisting of alkyl having at least 2 carbon atoms, amino, alkenyl,alkynyl, arylkyl, and silyl. The ligand L is coordinated to a metal Mhaving an atomic number greater than 40. Preferably, M is Ir.

In one aspect, the compound has the formula:

L′ is an ancillary ligand. m is 1, 2, or 3.

In another aspect, L′ is a monoanionic bidentate ligand. In yet anotheraspect, L′ is

R₁, R₂, and R₃ are independently selected from the group consisting ofhydrogen, deuterium, alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl,aryl and heteroaryl.

In one aspect, the compound has the formula:

wherein R₁, R₂, R₃, R₅, R₆ and R₇ are independently selected from thegroup consisting of hydrogen, deuterium, alkyl, silyl, alkoxy, amino,alkenyl, alkynyl, arylkyl, aryl and heteroaryl. R₄ is selected from thegroup consisting of alkyl having at least 2 carbon atoms, amino,alkenyl, alkynyl, arylkyl, and silyl. m is 1, 2, or 3. Preferably, eachof R₁ and R₃ are a branched alkyl with branching at a position furtherthan the α position to the carbonyl group.

In one aspect, each of R₅, R₆ and R₇ are independently selected frommethyl and hydrogen, and at least one of R₅, R₆ and R₇ is methyl. Inanother aspect, each of R₅ and R₇ are methyl, and R₆ is hydrogen. In yetanother aspect, each of R₅ and R₆ are methyl, and R₇ is hydrogen. In afurther aspect, each of R₅, R₆ and R₇ are methyl.

In one aspect, R₄ is an alkyl group having at least 4 carbon atoms. Inanother aspect, R₄ is an alkyl group having at least 3 carbon atoms.

Specific, non-limiting examples of the 5-substituted 2-phenylquinolinecontaining compounds are provided. In one aspect, the compound isselected from the group consisting of Compound 1-Compound 50.

In one aspect, R₄ comprises a cycloalkyl group having at least 4 carbonatoms. Specific, non-limiting examples of the 5-substituted2-phenylquinoline containing compound having Formula III wherein R₄comprises a cycloalkyl group having at least 4 carbon atoms is selectedfrom the group consisting of Compound II-1-Compound II-72.

Additionally, a first device comprising an organic light emitting deviceis provided. The organic light emitting device further comprises ananode, a cathode; and an organic layer, disposed between the anode andthe cathode. The organic layer comprises a compound comprising a ligandL having Formula I.

A is a 5-membered or 6-membered carbocyclic or heterocyclic ring.Preferably, A is phenyl. R_(A) may represent mono, di, tri, or tetrasubstitutions. Each of R_(A) is independently selected from the groupconsisting of hydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl,aryl and heteroaryl. R_(B) is selected from the group consisting ofalkyl having at least 2 carbon atoms, amino, alkenyl, alkynyl, arylkyl,and silyl. The ligand L is coordinated to a metal M having an atomicnumber greater than 40. Preferably, M is Ir.

Specific, non-limiting examples of devices comprising the compounds areprovided. In one aspect, the compound used in the first device isselected from the group consisting of Compound 1-Compound 50.

The various specific aspects discussed above for compounds comprising aligand L having Formula I are also applicable to a compound comprising aligand L having Formula I that is used in the first device. Inparticular, specific aspects of R_(A), R_(B), A, L′, M, m, R₁, R₂, R₃,R₄, R₅, R₆, and R₇ of the compound comprising a ligand L having FormulaI discussed above are also applicable to a compound comprising a ligandL having Formula I that is used in a the first device.

In one aspect, the organic layer is an emissive layer and the compoundis an emissive dopant. In another aspect, the organic layer furthercomprises a host. In yet another aspect, the host is a metal8-hydroxyquinolate. Preferably, the host is:

In one aspect, the first device is a consumer product. In anotheraspect, the first device is an organic light emitting device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows an exemplary compound comprising a 5-substituted2-phenylquinoline ligand (top) and a preferred embodiment of the5-substituted 2-phenylquinolone compound (bottom).

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order. The properties and functions of thesevarious layers, as well as example materials, are described in moredetail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporatedby reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink-jet and OVJD.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processability than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Many of the devices are intended for use in a temperaturerange comfortable to humans, such as 18 degrees C. to 30 degrees C., andmore preferably at room temperature (20-25 degrees C.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl,heterocyclic group, aryl, aromatic group, and heteroaryl are known tothe art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32,which are incorporated herein by reference. Novel organometallic2-phenylquinoline Ir complexes are provided. In particular, thecompounds comprise an alkyl having at least 2 carbon atoms. It isbelieved that compounds containing a bulky alkyl at the 5-position onthe phenylquinoline is novel. In addition, it is believed that thepresence of a bulky alkyl at the 5-position may increase efficiency bypreventing self-quenching. Notably, placing the bulky alkyl at the5-position on the 2-phenylquinoline does not shift the emissionwavelength or change the color. Therefore, these compounds may provideimproved efficiency and maintain saturated red emission. These compoundsmay be useful in organic light emitting devices, in particular as redemitters in the emissive layer of such devices.

Compounds comprising a 5-substituted 2-phenylquinoline containing ligandare provided. The compounds comprise a ligand L having the formula:

A is a 5-membered or 6-membered carbocyclic or heterocyclic ring.Preferably, A is phenyl. R_(A) may represent mono, di, tri, or tetrasubstitutions. Each of R_(A) is independently selected from the groupconsisting of hydrogen, deuterium, alkyl, silyl, alkoxy, amino, alkenyl,alkynyl, arylkyl, aryl and heteroaryl. These compounds may be fully orpartially deuterated. R_(B) is selected from the group consisting ofalkyl having at least 2 carbon atoms, amino, alkenyl, alkynyl, arylkyl,and silyl. The ligand L is coordinated to a metal M having an atomicnumber greater than 40. Preferably, M is Ir.

In one aspect, the compound has the formula:

L′ is an ancillary ligand. m is 1, 2, or 3.

In another aspect, L′ is a monoanionic bidentate ligand. In yet anotheraspect, L′ is

R₁, R₂, and R₃ are independently selected from the group consisting ofhydrogen, deuterium, alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl,aryl and heteroaryl.

In one aspect, the compound has the formula:

R₁, R₂, R₃, R₅, R₆ and R₇ are independently selected from the groupconsisting of hydrogen, deuterium, alkyl, silyl, alkoxy, amino, alkenyl,alkynyl, arylkyl, aryl and heteroaryl. R₄ is selected from the groupconsisting of alkyl having at least 2 carbon atoms, amino, alkenyl,alkynyl, arylkyl, and silyl. m is 1, 2, or 3.

Preferably, each of R₁ and R₃ are a branched alkyl with branching at aposition further than the α position to the carbonyl group. Withoutbeing bound by theory, it is believed that a branched alkyl substituentat R₁ and R₃ may provide high device efficiency and stability, and avery narrow emission spectrum.

The placement of substituents on the compound having Formula III mayimprove efficiency while maintaining a desirable spectrum. Inparticular, it is believed that substitution on the position ortho tothe R₅ next to quinoline with a substituent other than hydrogen, asshown in Formula III, may result in broadening the compound's spectrum.In addition, alkyl substitution on quinoline at the 3-position maybroaden the emission spectrum. Alkyl substitution at the 4, 6, or7-position may slightly blue shift the emission spectrum, thereby makingthe emission less saturated. Therefore, the substitution pattern of the5-substituted 2-phenylquinoline compounds described herein may providehighly desirable compound and device characteristics.

In one aspect, each of R₅, R₆ and R₇ are independently selected frommethyl and hydrogen, and at least one of R₅, R₆ and R₇ is methyl. Inanother aspect, each of R₅ and R₇ are methyl, and R₆ is hydrogen. In yetanother aspect, each of R₅ and R₆ are methyl, and R₇ is hydrogen. In afurther aspect, each of R₅, R₆ and R₇ are methyl.

In one aspect, R₄ is an alkyl group having at least 4 carbon atoms. Inanother aspect, R₄ is an alkyl group having at least 3 carbon atoms.

Alkyl substitutions may be particularly important because they offer awide range of tunability in terms of evaporation temperature,solubility, energy levels, device efficiency and narrowness of theemission spectrum. Additionally, alkyl groups can be stable functionalgroups chemically and in device operation.

Specific, non-limiting examples of the 5-substituted 2-phenylquinolinecontaining compounds are provided. In one aspect, the compound isselected from the group consisting of:

In another aspect, R₄ in compound having Formula III comprises acycloalkyl group having at least 4 carbon atoms. The inventors havediscovered that provision of cycloalkyl substituent at 5-position of the2-phenylquinoline provides further improvement in the phosphorescentcharacteristics of the compound over linear or branched alkyl groupsubstituents. This improved compound is suitable as red emitters inPhosphorescent OLEDs. Specific, non-limiting examples of the5-substituted 2-phenylquinoline containing compound having Formula IIIwherein R₄ comprises a cycloalkyl group having at least 4 carbon atomsis selected from the group consisting of Compound II-1-Compound II-72shown below. In another aspect, R₄ is a cyloalkyl. In one embodiment, R₄is a cyclopentyl or cyclohexyl.

Additionally, a first device comprising an organic light emitting deviceis provided. The organic light emitting device further comprises ananode, a cathode, and an organic layer, disposed between the anode andthe cathode. The organic layer comprises a compound comprising a ligandL having the formula:

A is a 5-membered or 6-membered carbocyclic or heterocyclic ring.Preferably, A is phenyl. R_(A) may represent mono, di, tri, or tetrasubstitutions. Each of R_(A) is independently selected from the groupconsisting of hydrogen, deuterium, alkyl, silyl, alkoxy, amino, alkenyl,alkynyl, arylkyl, aryl and heteroaryl. R_(B) is selected from the groupconsisting of alkyl having at least 2 carbon atoms, amino, alkenyl,alkynyl, arylkyl, and silyl. The ligand L is coordinated to a metal Mhaving an atomic number greater than 40. Preferably, M is Ir.

In one aspect, the compound has the formula:

L′ is an ancillary ligand. m is 1, 2, or 3.

In one aspect, L′ is a monoanionic bidentate ligand. In another aspect,L′ is

R₁, R₂, and R₃ are independently selected from the group consisting ofhydrogen, deuterium, alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl,aryl and heteroaryl.

In one aspect, the compound has the formula:

R₁, R₂, R₃, R₅, R₆ and R₇ are independently selected from the groupconsisting of hydrogen, deuterium, alkyl, silyl, alkoxy, amino, alkenyl,alkynyl, arylkyl, aryl and heteroaryl. R₄ is selected from the groupconsisting of alkyl having at least 2 carbon atoms, amino, alkenyl,alkynyl, arylkyl, and silyl. m is 1, 2, or 3.

Specific, non-limiting examples of devices comprising the compounds areprovided. In one aspect, the first device comprises a compound selectedfrom the group consisting of Compound 1-Compound 50.

In another aspect, the organic layer comprises a compound having FormulaIII wherein R₄ is a cycloalkyl group having at least 4 carbon atoms.Specific, non-limiting examples of the compound having Formula IIIwherein R₄ is a cycloalkyl group having at least 4 carbon atoms isselected from the group consisting of Compound II-1-Compound II-72disclosed herein.

In one aspect, the organic layer is an emissive layer and the compoundis an emissive dopant. In another aspect, the organic layer furthercomprises a host. In yet another aspect, the host is a metal8-hydroxyquinolate. Preferably, the host is:

In one aspect, the first device is a consumer product. In anotheraspect, the first device is an organic light emitting device.

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

HIL/HTL:

A hole injecting/transporting material to be used in embodiments of thepresent invention is not particularly limited, and any compound may beused as long as the compound is typically used as a holeinjecting/transporting material. Examples of the material include, butare not limited to: a phthalocyanine or porphryin derivative; anaromatic amine derivative; an indolocarbazole derivative; a polymercontaining fluorohydrocarbon; a polymer with conductivity dopants; aconducting polymer, such as PEDOT/PSS; a self-assembly monomer derivedfrom compounds such as phosphonic acid and sliane derivatives; a metaloxide derivative, such as MoO_(x); a p-type semiconducting organiccompound, such as 1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; ametal complex, and a cross-linkable compounds.

Examples of aromatic amine derivatives used in the HIL or HTL include,but are not limited to, the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting aromatichydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl,triphenylene, naphthalene, anthracene, phenalene, phenanthrene,fluorene, pyrene, chrysene, perylene, azulene; group consisting aromaticheterocyclic compounds such as dibenzothiophene, dibenzofuran,dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene,benzoselenophene, carbazole, indolocarbazole, pyridylindole,pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole,oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine,pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine,indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole,benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline,quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine,phenazine, phenothiazine, phenoxazine, benzofuropyridine,furodipyridine, benzothienopyridine, thienodipyridine,benzoselenophenopyridine, and selenophenodipyridine; and groupconsisting 2 to 10 cyclic structural units which are groups of the sametype or different types selected from the aromatic hydrocarbon cyclicgroup and the aromatic heterocyclic group and are bonded to each otherdirectly or via at least one of oxygen atom, nitrogen atom, sulfur atom,silicon atom, phosphorus atom, boron atom, chain structural unit and thealiphatic cyclic group. Wherein each Ar is further substituted by asubstituent selected from the group consisting of hydrogen, deuterium,alkyl, alkoxy, amino, alkenyl, alkynyl, arylalkyl, heteroalkyl, aryl andheteroaryl.

In one aspect, Ar¹ to Ar⁹ is independently selected from the groupconsisting of:

k is an integer from 1 to 20; X¹ to X⁸ is CH or N; Ar¹ has the samegroup defined above.

Examples of metal complexes used in the HIL or HTL include, but are notlimited to, the following general formula:

M is a metal, having an atomic weight greater than 40; (Y¹-Y²) is abidentate ligand, Y1 and Y² are independently selected from C, N, O, P,and S; L is an ancillary ligand; m is an integer value from 1 to themaximum number of ligands that may be attached to the metal; and m+n isthe maximum number of ligands that may be attached to the metal.

In one aspect, (Y¹-Y²) is a 2-phenylpyridine derivative.

In another aspect, (Y¹-Y²) is a carbene ligand.

In another aspect, M is selected from Ir, Pt, Os, and Zn.

In a further aspect, the metal complex has a smallest oxidationpotential in solution vs. Fc⁺/Fc couple less than about 0.6 V.

Host:

The light emitting layer of the organic EL device in some embodimentsthe present invention preferably contains at least a metal complex aslight emitting material, and may contain a host material using the metalcomplex as a dopant material. Examples of the host material are notparticularly limited, and any metal complexes or organic compounds maybe used as long as the triplet energy of the host is larger than that ofthe dopant.

Examples of metal complexes used as hosts are preferred to have thefollowing general formula:

M is a metal; (Y³-Y⁴) is a bidentate ligand, Y³ and Y⁴ are independentlyselected from C, N, O, P, and S; L is an ancillary ligand; m is aninteger value from 1 to the maximum number of ligands that may beattached to the metal; and m+n is the maximum number of ligands that maybe attached to the metal.

In one aspect, the metal complexes are:

(O—N) is a bidentate ligand, having metal coordinated to atoms O and N.

In another aspect, M is selected from Ir and Pt.

In a further aspect, (Y³-Y⁴) is a carbene ligand.

Examples of organic compounds used as hosts are selected from the groupconsisting aromatic hydrocarbon cyclic compounds such as benzene,biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene,phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; groupconsisting aromatic heterocyclic compounds such as dibenzothiophene,dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran,benzothiophene, benzoselenophene, carbazole, indolocarbazole,pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole,oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole,pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine,oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine,benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline,cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine,pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine,benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine;and group consisting 2 to 10 cyclic structural units which are groups ofthe same type or different types selected from the aromatic hydrocarboncyclic group and the aromatic heterocyclic group and are bonded to eachother directly or via at least one of oxygen atom, nitrogen atom, sulfuratom, silicon atom, phosphorus atom, boron atom, chain structural unitand the aliphatic cyclic group. Wherein each group is furthersubstituted by a substituent selected from the group consisting ofhydrogen, deuterium, alkyl, alkoxy, amino, alkenyl, alkynyl, arylalkyl,heteroalkyl, aryl and heteroaryl.

In one aspect, the host compound contains at least one of the followinggroups in the molecule:

R¹ to R⁷ is independently selected from the group consisting ofhydrogen, deuterium, alkyl, alkoxy, amino, alkenyl, alkynyl, arylalkyl,heteroalkyl, aryl and heteroaryl, when it is aryl or heteroaryl, it hasthe similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from CH or N.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies as compared to a similar device lacking a blocking layer.Also, a blocking layer may be used to confine emission to a desiredregion of an OLED.

In one aspect, the compound used in the HBL contains the same moleculeused as host described above.

In another aspect, the compound used in the HBL contains at least one ofthe following groups in the molecule:

k is an integer from 0 to 20; L is an ancillary ligand, m is an integerfrom 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable oftransporting electrons. Electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

In one aspect, the compound used in the ETL contains at least one of thefollowing groups in the molecule:

R¹ is selected from the group consisting of hydrogen, deuterium, alkyl,alkoxy, amino, alkenyl, alkynyl, arylalkyl, heteroalkyl, aryl andheteroaryl, when it is aryl or heteroaryl, it has the similar definitionas Ar's mentioned above.

Ar¹ to Ar³ has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from CH or N.

In another aspect, the metal complexes used in the ETL contain, but arenot limited to, the following general formula:

(O—N) or (N—N) is a bidentate ligand, having metal coordinated to atomsO, N or N, N; L is an ancillary ligand; m is an integer value from 1 tothe maximum number of ligands that may be attached to the metal.

In any above-mentioned compounds used in each layer of OLED device, thehydrogen atoms can be partially or fully deuterated.

In addition to and/or in combination with the materials disclosedherein, many hole injection materials, hole transporting materials, hostmaterials, dopant materials, exiton/hole blocking layer materials,electron transporting and electron injecting materials may be used in anOLED. Non-limiting examples of the materials that may be used in an OLEDin combination with materials disclosed herein are listed in Table 1below. Table 1 lists non-limiting classes of materials, non-limitingexamples of compounds for each class, and references that disclose thematerials.

TABLE 1 MATERIAL EXAMPLES OF MATERIAL PUBLICATIONS Hole injectionmaterials Phthalocyanine and porphryin compounds

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EXPERIMENTAL Compound Examples Example 1. Synthesis of Compound 1

Synthesis of (2-amino-6-chlorophenyl)methanol

2-Amino-6-chlorobenzoic acid (25.0 g, 143 mmol) was dissolved in 120 mLof anhydrous THF in a 500 mL 2 neck round bottom flask. The solution wascooled in an ice-water bath. 215 mL of 1.0 M lithium aluminum hydride(LAH) THF solution was then added dropwise. After all of the LAH wasadded, the reaction mixture was allowed to warm up to room temperatureand then stirred at room temperature overnight. ˜10 mL of water wasadded to the reaction mixture followed by 7 g 15% NaOH. An additional 20g of water was added to the reaction mixture. The organic THF phase wasdecanted and ˜200 mL of ethyl acetate was added to the solid withstirring. Na₂SO₄ was added as a drying agent to the combined ethylacetate organic portion and THF portion. The mixture was filtered andevaporated. ˜20 g yellow solid was obtained and taken on to the nextstep without further purification.

Synthesis of 5-chloro-2-(3,5-dimethylphenyl)quinoline

(2-Amino-6-chlorophenyl)methanol (16 g, 102 mmol),3,5-dimethylacetophenone (22.6 g, 152 mmol), RuCl₂(PPh₃)₃ (0.973 g,1.015 mmol), and KOH (10.25 g, 183 mmol) were refluxed in 270 mL oftoluene for 18 h. Water was collected from the reaction using aDean-stark trap. The reaction mixture was allowed to cool to roomtemperature, filtered through a silica gel plug and eluted with 5% ethylacetate in hexanes. The product was further purified by Kugelrohrdistillation to give 23.5 g of crude product, which was crystallizedfrom 60 mL of MeOH to give 8.6 g (32% yield) of the desired product.

Synthesis of 2-(3,5-dimethylphenyl)-5-isobutylquinoline

5-Chloro-2-(3,5-dimethylphenyl)quinoline (4.3 g, 16.06 mmol),isobutylboronic acid (3.2 g, 31.4 mmol),dicyclohexyl(2′,6′-dimethoxy-[1,1′-biphenyl]-2-yl)phosphine (0.538 g,1.31 mmol), and potassium phosphate monohydrate (18.3 g, 79 mmol) weremixed in 114 mL of toluene. The system was degassed for 20 minutes.Pd₂(dba)₃ was then added and the system was refluxed overnight. Aftercooling to room temperature, the reaction mixture was filtered through aCelite® plug and eluted with dichloromethane. The product was furtherpurified by a Kugelrohr distillation and then further purified by columnchromatography using 5% ethyl acetate in hexanes. This was followed byanother Kugelrohr distillation to give 3.2 g (72% yield) of product.

Synthesis of Iridium Dimer

A mixture of 2-(3,5-dimethylphenyl)-5-isobutylquinoline (3.2 g, 11.06mmol), IrCl₃.4H₂O (1.79 g, 4.83 mmol), 2-ethoxyethanol (45 mL) and water(105 mL) was refluxed under nitrogen overnight. The reaction mixture wasfiltered and washed with MeOH (3×10 mL). ˜2.9 g of dimer was obtainedafter vacuum drying. The dimer was used for the next step withoutfurther purification.

Synthesis of Compound 1

Dimer (2.9 g, 1.80 mmol), pentane-2,4-dione (1.80 g, 18.02 mmol), K₂CO₃(2.49 g, 18.02 mmol) and 2-ethoxyethanol (22 mL) were stirred at roomtemperature for 24 h. The precipitate was filtered and washed withmethanol. The solid was further purified by passing it through a silicagel plug (that was pretreated with 15% triethylamine (TEA) in hexanesand eluted with methylene chloride. 2-Propanol was added to thefiltrate. The filtrate was concentrated, but not to dryness. 1.6 g ofproduct was obtained after filtration. The solid was sublimed twiceunder high vacuum at 240° C. to give 1.0 g (64%) of Compound 1.

Synthesis of Compound II-2 Synthesis of5-cyclopentyl-2-(3,5-dimethylphenyl)quinoline

5-Chloro-2-(3,5-dimethylphenyl)quinoline (14.0 g, 52.3 mmol) and[1,3-bis(diphenylphosphino)propane]-dichloronickel (II) (0.10 g, 0.19mmol) were dissolved in 250 mL of anhydrous diethyl ether under N₂ atm.The reaction mixture was degassed and solution of cyclopentylmagnesiumiodide (2 M solution in ether, 52 ml, 105 mmol) was added dropwise. Thereaction mixture was stirred for 1 h, quenched with 20% aq. solution ofammonium chloride and extracted with ethyl acetate. The organic solutionwas dried over sodium sulfate, filtered and evaporated, providing yellowsolid. Purification with column chromatography on silica gel, elutedwith hexane/ethyl acetate 9/1 (v/v) mixture followed by crystallizationfrom heptanes provided 5-cyclopentyl-2-(3,5-dimethylphenyl)quinoline ascolorless crystals (12 g, 76% yield).

Synthesis of Ir(III) Dimer

5-Cyclopentyl-2-(3,5-dimethylphenyl)quinoline (3.56 g, 11.8 mmol) andiridium(III) chloride trihydrate (1.30 g, 3.69 mmol) were dissolved inthe mixture of ethoxyethanol (90 mL) and water (30 mL). Reaction mixturewas degassed and heated to 105° C. for 24 h. The reaction mixture wasthen cooled down to room temperature and filtered through filter paper.The filtrate was washed with methanol and dried in vacuum, providingiridium complex dimer as dark solid 1.60 g (54% yield).

Synthesis of Compound II-2

Iridium complex dimer (2.17 g, 1.31 mmol), acetylacetonate (1.31 g, 13.1mmol) and potassium carbonate (1.81 g, 13.1 mmol) were suspended in 70mL of ethoxyethanol, and stirred overnight under N₂ at room temperature.The reaction mixture was then filtered through a pad of Celite®, washedwith MeOH. Most of the red material was solubilized and passed throughthe Celite®. The Celite® was suspended in DCM, containing 10% oftriethylamine and this suspension was combined with filtrate andevaporated. The residue was purified by column chromatography on silicagel, pre-treated with Et₃N, eluted with hexane/dichloromethane mixture,providing a dark red solid. The product was further purified byrecrystallizing from dichloromethane and isopropanol mixture to givedesired product (1.67 g, 72% yield).

Device Examples

All example devices were fabricated by high vacuum (<10⁻⁷ Torr) thermalevaporation. The anode electrode is 1200 Å of indium tin oxide (ITO).The cathode consisted of 10 Å of LiF followed by 1000 Å of Al. Alldevices are encapsulated with a glass lid sealed with an epoxy resin ina nitrogen glove box (<1 ppm of H₂O and O₂) immediately afterfabrication, and a moisture getter was incorporated inside the package.

The organic stack of the device examples consisted of sequentially, fromthe 1200 Å ITO surface, 100 Å of Compound A as the hole injection layer(HIL), 400 Å of 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD)as the hole transporting layer (HTL), 300 Å of the 7 wt % inventioncompound doped into BAlq host as the emissive layer (EML), 550 Å of Alq₃(tris-8-hydroxyquinoline aluminum) as the ETL.

Comparative Examples were fabricated similarly to the Device Examplesexcept that Compound B, C or D was used as the emitter in the EML.

As used herein, the following compounds have the following structures:

Particular emissive dopants for the emissive layer of an OLED areprovided. These compounds may lead to devices having particularly goodproperties.

The device structures and device data are summarized in Table 2.

TABLE 2 At 1,000 nits At 40 mA/cm² 1931 CIE λ_(max) FWHM V LE EQE PEcd/A per L₀ LT_(80%) [h] Emitter x y [nm] [nm] [V] [cd/A] [%] [lm/W] EQE[nits] RT 70° C. Compound 1 0.666 0.331 622 58 7.8 22.2 20.5 9.0 1.086,852 600 66 (Device Example) Compound B 0.667 0.331 622 62 8.1 19.918.8 7.7 1.06 6,447 878 70 (Comparative Example) Compound C 0.662 0.335620 58 7.4 21.9 18.9 9.3 1.16 6,927 565 73 (Comparative Example)Compound D 0.664 0.334 620 64 8.1 21.1 19.4 8.1 1.09 6,666 321 44(Comparative Example)

As seen from the Table 2, the EQE of Compound 1 at 1000 nits is up to10% higher than Compounds B, C, and D. Additionally, the EL spectralfull width at half maximum (FWHW) of Compound 1 (58 nm) is also narrowerthan Compound B (62 nm) and Compound D (64 nm), which is a desirabledevice property. The FWHM of Compound 1 is the same as the FWHM ofCompound C (58 nm). The color saturation (CIE) of Compound 1 andCompound B are also the same. These results indicate that Compound 1 isa more efficient red emitter than Compounds B, C and D with a desirablenarrower FWHM.

Compound 1 also has almost a double lifetime at room temperaturecompared to Compound D. The only difference between these two compoundsis that Compound 1 has a bulkier group at 5-position. This clearlyindicates that a bulkier group than methyl in the 5-position of2-phenylquinoline may indeed provide a significant improvement inoverall device performance.

Additional Device Examples

Additional device examples were fabricated to evaluate the compoundhaving Formula III wherein R₄ comprises a cycloalkyl group. Theseadditional example devices were fabricated by high vacuum (<10⁻⁷ Torr)thermal evaporation. The anode electrode is 1200 Å of ITO. The cathodeconsisted of 10 Å of LiF followed by 1,000 Å of Al. All devices areencapsulated with a glass lid sealed with an epoxy resin in a nitrogenglove box (<1 ppm of H₂O and O₂) immediately after fabrication, and amoisture getter was incorporated inside the package.

The organic stack of the additional device examples consisted ofsequentially, from the ITO surface, 100 Å of Compound A as the HIL, 400Å of 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD) as the HTL,300 Å of the invention compound doped in Balq as host with 6 wt % of anIr phosphorescent compound as the EML, 550 Å of Alq₃(tris-8-hydroxyquinoline aluminum) as the ETL.

The device structures and device data from the additional deviceexamples are summarized in Table 3 below.

TABLE 3 At 1000 nits Alq 1931 CIE λ max FWHM Volt LE EQE PE cd/AperEmitter [Å] x y [nm] [nm] [V] [cd/A] [%] [lm/W] EQE Compound II-2 550 Å0.662 0.335 620 60 8.3 23.2 20.4 8.8 1.1

As can be seen from Table 3, the example device with Compound II-2showed saturated red color and high luminous efficiency. The LE wasmeasured at 23.2 cd/A compared to 22.2 cd/A for Compound 1.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

The invention claimed is:
 1. A compound comprising a ligand L having theformula:

wherein each of R₅, R₆, and R₇ is independently selected from the groupconsisting of hydrogen, deuterium, alkyl, silyl, alkoxy, amino, alkenyl,alkynyl, arylkyl, aryl and heteroaryl; wherein R₄ is selected from thegroup consisting of isopropyl, isobutyl, and t-butyl; and wherein theligand L is coordinated to a metal M having an atomic number greaterthan
 40. 2. The compound of claim 1, wherein M is Ir.
 3. The compound ofclaim 1, wherein the compound has the formula Ir(L)_(m)(L′)_(3-m)wherein L′ is an ancillary ligand; and wherein m is 1, 2, or
 3. 4. Thecompound of claim 3, wherein L′ is a monoanionic bidentate ligand. 5.The compound of claim 3, wherein the compound has the formula

and wherein R₁, R₂, and R₃ are independently selected from the groupconsisting of hydrogen, deuterium, alkyl, alkoxy, amino, alkenyl,alkynyl, arylkyl, aryl and heteroaryl.
 6. The compound of claim 5,wherein each of R₁ and R₃ are a branched alkyl with branching at aposition further than the α position to the carbonyl group.
 7. Thecompound of claim 5, wherein each of R₅, R₆ and R₇ are independentlyselected from methyl and hydrogen, and at least one of R₅, R₆ and R₇ ismethyl.
 8. The compound of claim 5, wherein each of R₅ and R₇ is methyl,and R₆ is hydrogen.
 9. The compound of claim 5, wherein each of R₅ andR₆ is methyl, and R₇ is hydrogen.
 10. The compound of claim 5, whereineach of R₅, R₆ and R₇ is methyl.
 11. The compound of claim 1, wherein R₄is isopropyl.
 12. The compound of claim 1, wherein R₄ is isobutyl. 13.The compound of claim 1, wherein R₄ is t-butyl.
 14. The compound ofclaim 1, wherein the compound is selected from the group consisting of:


15. The compound of claim 1, wherein the compound is selected from thegroup consisting of:


16. The compound of claim 1, wherein the compound is selected from thegroup consisting of:


17. A first device comprising an organic light emitting device,comprising: an anode; a cathode; and an organic layer, disposed betweenthe anode and the cathode, comprising a compound comprising a ligand Lhaving the formula:

wherein each of R₅, R₆, and R₇ is independently selected from the groupconsisting of hydrogen, deuterium, alkyl, silyl, alkoxy, amino, alkenyl,alkynyl, arylkyl, aryl and heteroaryl; wherein R₄ is selected from thegroup consisting of isopropyl, isobutyl, and t-butyl; and wherein theligand L is coordinated to a metal M having an atomic number greaterthan
 40. 18. The first device of claim 17, wherein the organic layer isan emissive layer and the compound is an emissive dopant.
 19. The firstdevice of claim 18, wherein the organic layer further comprises a host.20. A consumer product comprising an organic light emitting device,comprising: an anode; a cathode; and an organic layer, disposed betweenthe anode and the cathode, comprising a compound comprising a ligand Lhaving the formula:

wherein each of R₅, R₆, and R₇ is independently selected from the groupconsisting of hydrogen, deuterium, alkyl, silyl, alkoxy, amino, alkenyl,alkynyl, arylkyl, aryl and heteroaryl; wherein R₄ is selected from thegroup consisting of isopropyl, isobutyl, and t-butyl; and wherein theligand L is coordinated to a metal M having an atomic number greaterthan
 40. 21. The consumer product of claim 20, wherein the consumerproduct is selected from the group consisting of a flat panel display, acomputer monitor, a television, a billboard, lights for interior orexterior illumination and/or signaling, a heads up display, a fullytransparent display, a flexible display, a laser printer, a telephone, acell phone, a personal digital assistant (PDA), a laptop computer, adigital camera, a camcorder, a viewfinder, a micro-display, a vehicle,an area wall, theater or stadium screen, or a sign.